Probably the most common thing that has always been mentioned is the scarcity. Gold and bitcoin has a limited supply and both are used for something in the life, there is always a requirement for it.
I would not agree that Bitcoin and gold can be compared when it comes to total supply, because we know that Bitcoin is limited to 21 million and this is a hard fact, but how many people can say how much gold is exists in the world today, whether it is gold that has been mined or what is still underground. I think that I read some time ago that all mined gold can be stored in size of the three Olympic pools. But what about gold on other planets, on asteroids?
The main advantages that BTC has over gold is publicly known total supply, followed by a pre-set mining procedure which include halvings/block rewards. There is also an ease of transfer when it comes to BTC, whether it be payment transactions or transferring value. Take 1 kg of gold and try to move it through customs, and take 100 BTC in hardware wallet or as a seed on a piece of paper or in your head (it is not hard to memorize 12 words).
Furthermore, the possibility of counterfeiting BTC is zero if we do not count forks, and gold bars/coins are very easily forged, gold on the outside, lead on the inside.
Should BTC gain price stability, such as gold, it could be a serious competitor.